Bloc Québécois Leader Gilles Duceppe says his scheduled appearance Thursday before the chamber of commerce in Roberval, Que., was cancelled at the last minute, and he is blaming other parties — especially the Conservatives — for blackmailing organizers into scotching his speech.

Duceppe said he received an open invitation to speak before the city's chamber of commerce last August, with the date of his appearance to be confirmed later.

The business club and the Bloc confirmed the arrangement on Tuesday. It would cost $20 per person to attend a breakfast conference, slated for Thursday, during which Duceppe would give a short speech.

But on Wednesday, the chamber of commerce called back, saying the event was off. Organizers said they decided to cancel Duceppe's appearance in the interest of fairness, since no other party leaders agreed to speak in the community of about 10,000 residents located 250 kilometres north of Quebec City.

Duceppe accused the Conservatives of pressuring the chamber to cancel it, describing the move as "shameful blackmail."

"Everything had been finalized," Duceppe said Thursday. "It's unacceptable. These tactics are totally unacceptable in a democracy."

In a statement issued late Thursday, the Roberval Chamber of Commerce said "outside pressures" prompted its executive committee to cancel the breakfast meeting because of concerns it would compromise the group's political impartiality.

The statement didn't specify what the pressures were, but it did say that the committee had acted precipitately and that it was a "mistake" to scrap Duceppe's speech.